In a vapour compression system, such as a refrigeration system, an air conditions system, a heat pump etc., a fluid medium, such as refrigerant, is alternatingly compressed by means of one or more compressors and expanded by means of one or more expansion devices, and heat exchange between the fluid medium and the ambient takes place in one or more heat rejecting heat exchangers, e.g. in the form of condensers or gas coolers, and in one or more heat absorbing heat exchangers, e.g. in the form of evaporators.
When refrigerant passes through an evaporator arranged in a vapour compression system, the refrigerant is at least partly evaporated while heat exchange takes place with the ambient or with a secondary fluid flow across the evaporator, in such a manner that heat is absorbed by the refrigerant passing through the evaporator. The heat transfer between the refrigerant and the ambient or the secondary fluid flow is most efficient along a part of the evaporator which contains liquid refrigerant. Accordingly, it is desirable to operate the vapour compression system in such a manner that liquid refrigerant is present in as large a part of the evaporator as possible, preferably along the entire evaporator.
However, if liquid refrigerant reaches the compressor unit, there is a risk that the compressor(s) of the compressor unit is/are damaged. In order to avoid this, it is necessary to either operate the vapour compression system in such a manner that liquid refrigerant is not allowed to pass through the evaporator, or to ensure that any liquid refrigerant which passes through the evaporator is removed from the suction line, and is thereby prevented from reaching the compressor unit.
WO 2012/168544 A1 discloses a multi-evaporator refrigeration circuit comprising at least a compressor, a condenser or gas cooler, a first throttling valve, a liquid/vapour separator, a pressure limiting valve, a liquid level sensing device, at least one evaporator and a suction receiver. In the refrigeration circuit at least one ejector comprising a suction port is included in parallel to the first throttling valve. The refrigeration system is adapted to drive cold liquid from the suction receiver to the suction port of the ejector. A first control valve in the line from the suction receiver to the suction port of the ejector can be opened, based on a maximum level signal generated by the liquid level sensing device, whenever the level of liquid refrigerant in the suction receiver is above a set maximum level.